1. Field of the Invention
The present invention relates to a device for making a thin film on a substrate through a method of Facing Targets Sputtering.
2. Description of the Prior Art
There are known a vacuum deposition method, a sputtering method etc. as methods for forming thin films. The sputtering method is widely used for forming a thin film on a substrate made of PMMA because of intimacy between the substrate and the thin film formed therethrough. The amorphous thin film of rare earth--transition metal alloy formed through the sputtering method is applied to an erasable magneto-optical recording medium.
The sputtering method is performed as follows: Positive ions of an inert gas such as Argon (Ar) first created by a glow discharge are accelerated toward a cathode or target, and then they impinge upon the target. As a result of ionic bombardment, neutral atoms and ions are removed from the target surface into a vacuum chamber due to the exchange of momentum therebetween. The liberated or sputtered atoms and ions are consequently deposited on a preselected substrate disposed in the vacuum chamber.
FIG. 1 shows a conventional Facing Targets Sputtering device which accomplishes the sputtering method. As shown in FIG. 1, two target plates 5 are respectively connected and disposed onto two target holders 6 which are fixed to both inner ends of an air-tight container 1 so as to make the target plates 5 face each other. The target holders 6 are electrically isolated from the air-tight container 1. A pair of permanent magnets 8 are accommodated in the target holders 6 so as to create a magnetic field therebetween substantially perpendicular to the surface of the target plates 5. A substrate 11 is disposed closely to the magnetic field (which will define a plasma region 20) so as to preferably face it. A power source 10 is connected to the pair of the target plates 5 respectively. The air-tight container 1 is grounded. By applying a voltage across the container 1 and the target plates 5, a glow discharge is established between the container 1 and the plates 5. The intensity and extent of the established magnetic field can be controlled by regulating the magnitude of a current flowing through the coil 22 disposed around the air-tight container 1 at the outside.
The electrons emitted from the both target plates 5 by applying the voltage are confined between the target plates 5 because of the magnetic field to promote the ionization of the inert gas so as to form a plasma region 20. The positive ions of the inert gas existing in the plasma region 20 are accelerated toward the target plates 5, whereby those accelerated particles violently impinge upon the target plates 5. The bombardment of the target plates 5 by the accelerated particles of the inert gas and ions thereof causes atoms of the material forming the plates 5 to be emitted. The substrate 11 on which the thin film is to be disposed is placed around the plasma region 20, so that the bombardment of these high energy particles and ions against the thin film plane is avoided because of effective confinement of the plasma region 20 by the magnetic field.
In this way, the metallic atoms of the target plates 5 are deposited on the substrate 11 without unwanted temperature elevation of the substrate nor any defect in the formed thin film and/or damage on the surface of the substrate.
In such a Facing Targets Sputtering device, the composition of the alloy thin film can be changed either by replacing a plurality of targets different in composition from each other or by using a composite target which has a plurality of surface regions made of different metal materials.
However, it has been a problem in such a conventional Facing Targets Sputtering device that the replacement of the targets requires some tedious manual operations and takes too much time. Furthermore, it is not so easy to manufacture such a composite target.